The present invention is directed to vertebral stabilization of a spine using one or more rods anchored onto the vertebrae.
Back pain is one of the most common and often debilitating conditions affecting millions of people in all walks of life. Today, it is estimated that over ten million people in the United States alone suffer from persistent back pain. Approximately half of those suffering from persistent back pain are afflicted with chronic disabling pain, which seriously compromises a person's quality of life and is the second most common cause of worker absenteeism. Further, the cost of treating chronic back pain is very high, even though the majority of sufferers do not receive treatment due to health risks, limited treatment options and inadequate therapeutic results. Thus, chronic back pain has a significantly adverse effect on a person's quality of life, on industrial productivity, and on heath care expenditures.
Degenerative spinal column diseases, such as disc degenerative diseases (DDD), spinal stenosis, spondylolisthesis, and so on, need surgical operation if they do not take a turn for the better by conservative management.
Various methods of spinal immobilization have been known and used during this century in the treatment of spinal instability and displacement. One treatment for spinal stabilization is immobilization of the joint by surgical fusion, or arthrodesis. This method has been known since its development in 1911 by Hibbs and Albee. However, in many cases, and in particular, in cases involving fusion across the lumbosacral articulation and when there are many levels involved, pseudoarthrosis is a problem. It was discovered that immediate immobilization was necessary in order to allow a bony union to form.
Typically, spinal decompression is the first surgical procedure that is performed. The primary purpose of decompression is to reduce pressure in the spinal canal and on nerve roots located therein by removing a certain tissue of the spinal column to reduce or eliminate the pressure and pain caused by the pressure. If the tissue of the spinal column is removed the pain is reduced but the spinal column is weakened. Therefore, fusion surgery (e.g., ALIF, PLIF or posterolateral fusion) is often necessary for spinal stability following the decompression procedure. However, following the surgical procedure, fusion takes additional time to achieve maximum stability and a spinal fixation device is typically used to support the spinal column until a desired level of fusion is achieved. Depending on a patient's particular circumstances and condition, a spinal fixation surgery can sometimes be performed immediately following decompression, without performing the fusion procedure. The fixation surgery is performed in most cases because it provides immediate postoperative stability and, if fusion surgery has also been performed, it provides support of the spine until sufficient fusion and stability has been achieved.
Internal fixation refers to therapeutic methods of stabilization which are wholly internal to the patient. External fixation in contrast involves at least some portion of the stabilization device which is external to the patient's body. Internal fixation is advantageous since the patient is allowed greater freedom with the elimination of the external portion of the device and the possibility of infections, such as pin tract infection, is reduced.
Conventional methods of spinal fixation utilize a rigid spinal fixation device to support an injured spinal part and prevent movement of the injured part. These conventional spinal fixation devices include: fixing screws configured to be inserted into the spinal pedicle or sacral of the backbone to a predetermined depth and angle, rods or plates configured to be positioned adjacent to the injured spinal part, and coupling elements for connecting and coupling the rods or plates to the fixing screws such that the injured spinal part is supported and held in a relatively fixed position by the rods or plates.
A common problem with spinal fixation is the question of how to secure the fixation device to the spine without damaging the spinal cord. The pedicles are a favored area of attachment since they offer an area that is strong enough to hold the fixation device even when the patient suffers from osteoporosis. Since the middle 1950's, methods of fixation have utilized the pedicles. In early methods, screws extended through the facets into the pedicles. Posterior methods of fixation have been developed which utilize wires that extend through the spinal canal and hold a rod against the lamina (such as the Luque system).
U.S. Pat. No. 6,187,005 (the entire disclosure of which is hereby incorporated by reference) discloses a variable angle spinal fixation system, including a rod 16 positioned along a spinal column, a bone screw 14 having a threaded end for engaging a vertebra, and a connector member 86 for connecting the bone screw 14 and the rod 16. The connector member 86 has a channel extending through side surfaces of the connector member 86 for receiving the rod, an opening 108 laterally displaced from the channel and extending through top and bottom surfaces of the connector member 86 for receiving the bone screw 14, and a fastener clamping element 70 for securing the bone screw 14 in the opening 108 at a surgeon selected angle relative to the connector member 86 and rod 16. The connector member 86 also includes an opening 28 communicating with the channel and a clamping element 30 for securing the rod 16 in the channel.
Among the problems with the system of U.S. Pat. No. 6,187,005 is that the surgeon is required to manipulate two different clamping elements to fix the position of: (i) the bone screw 14 with respect to the connector member 86 (using the screw top 70), and (ii) the rod 16 with respect to the connector member 86 (using the set screw 30). This complicates the surgical procedure and increases the likelihood that a misalignment results during the tightening process.
U.S. Pat. No. 6,755,830 discloses a lateral connector with adjustable offset for a connection between a rod and a member for fixation to the spine, comprising a component to be connected to the fixation member and provided with an extension inserted into a second component which comprises a seat for the rod and a way to immobilize the rod and the extension when placed in contact with each other. The first component comprises a head with an opening with a bearing surface of articulation cooperating with a corresponding bearing surface of the fixation member. The second component comprises an orifice for receiving the extension, permitting rotation of the second component about the extension, with the orifice intersecting the bottom of the seat to form a slot. Among the problems with the apparatus of U.S. Pat. No. 6,755,830 is that the head of the bone screw may become easily disengaged from the first component through the side opening thereof.
Therefore, conventional spinal fixation devices have not provided a satisfactory solution to the problems associated with curing spinal diseases. Additionally, existing fixation devices utilize components that are not proven to provide long-term stability and durability, and are cumbersome and overly complex in terms of how they are adjusted and/or attach to the vertebral bones.